Temporal and morphological characteristics of high-frequency oscillations in an acute in vivo model of epilepsy.

Approximately 30% of patients with epilepsy do not respond to anti-epileptogenic drugs. Surgical removal of the epileptogenic zone (EZ), the brain regions where the seizures originate and spread, can be a possible therapy for these patients, but localizing the EZ is challenging due to a variety of clinical factors. High-frequency oscillations (HFOs) in intracranial electroencephalography (EEG) are a promising biomarker of the EZ, but it is currently unknown whether HFO rates and HFO morphology modulate as pathological brain networks evolve in a way that gives rise to seizures. To address this question, we assessed the temporal evolution of the duration of HFO events, amplitude of HFO events, and rates of HFOs per minute. HFO events were quantified using the 4AP in vivo rodent model of epilepsy, inducing seizures in two different brain areas. We found that the duration and amplitude of HFO events were significantly increased for the cortex model when compared to the hippocampus model. Additionally, the duration and amplitude increased significantly between baseline and pre-ictal HFOs in both models. On the other hand, the two models did not display a consistent increasing or decreasing trend in amplitude, duration or rate when comparing ictal and postictal intervals. Clinical Relevance- We assessed the amplitude, duration, and rate of HFOs in two acute in vivo rodent models of epilepsy. The significant modulation of HFO morphology from baseline to pre-ictal periods suggests that these features may be a robust biomarker for pathological tissue involved in epileptogenesis. Moreover, the differences in HFO morphology observed between cortex and hippocampus animal models possibly indicate that different structural network characteristics of the EZ cause this modulation. In all, we found that HFO features modulate significantly with the onset of seizures, further highlighting the need to consider of HFO morphology in EZ-localizing studies.

A chemogenetic approach for treating experimental Parkinson's disease.

BACKGROUND: PD is a common neurodegenerative disease primarily affecting the cortico-basal ganglia loop. OBJECTIVE: To investigate whether chemogenetic-mediated neuromodulation of various nuclei and pathways can counterbalance basal ganglia network abnormalities and improve motor disability in experimental PD. METHODS: Experimental PD was induced by stereotactic injection of 6-OHDA to the medial forebrain bundle. Designer receptors exclusively activated by designer drugs were expressed in different basal ganglia nuclei by stereotactic injections of adeno-associated viral vectors. We compared motor performance, monitored by the open-field and rotarod tests, after random and blinded application of either normal saline or the synthetic receptor activator, clozapine-N-oxide. RESULTS: Motor performance, as measured by movement velocity, rotations, and rotarod scores, were significantly improved in PD mice by enhancing the activity of the GPe with Gq custom receptors and by reducing basal ganglia output activity, targeting the output nuclei GPi and SNr with Gi custom receptors. CONCLUSION: Our findings support the hypothesis that enhanced inhibitory output activity of the basal ganglia complex underlie motor signs in PD, and point to the therapeutic potential of chemogenetic based treatments in PD patients. © 2018 International Parkinson and Movement Disorder Society.

Ultra Broad Band Neural Activity Portends Seizure Onset in a Rat Model of Epilepsy.

Epilepsy affects over 70 million people worldwide and 30% of patients' seizures cannot be controlled with medications, motivating the development of alternative therapies such as electrical stimulation. Current stimulation strategies attempt to stop seizures after they start, but none aim to prevent seizures altogether. Preventing seizures requires knowing when the brain is entering a preictal state (i.e., approaching seizure onset). Here we show that such preictal activity can be detected by an informative neural signal that progressively and monotonically changes as the brain approaches a seizure event. Specifically, we use local field potentials (LFP) from a rat model of epilepsy to develop an innovative measure of signal novelty relative to nonseizure activity, that shows the presence of progressive neural dynamics in an ultra broad band (4 Hz - 5 kHz). The measure is extracted from functional connectivity features computed from the LFPs which are used as an input to a one-class Support Vector Machine (SVM). The SVM outputs a scalar signal which quantifies how novel the current activity looks relative to baseline (non-seizure) activity and shows a progression towards seizure onset minutes ahead of time. The use of ultra broad band multivariate features into the SVM results in a novelty signal that has a significantly higher slope in the progression to seizure onset when compared to using power in conventional frequency bands (4 - 500 Hz) on individual channels as input features to the SVM. Functional connectivity in conjunction with the SVM is a strategy that generates a new measurement of novelty that can be used by closed-loop systems for seizure forecasting and prevention.

Localization of CHMP2B in postnatal rd1 mouse retina.

Retinitis pigmentosa is the most common form of inherited blindness in humans. A well-studied model of the disease is the rd1 mouse, characterized by a loss of function mutation in the catalytic ß subunit of the phosphodiesterase 6 (Pde6) holoenzyme involved in phototransduction within rods and cones. The period of photoreceptor degeneration in the rd1 mouse occurs during postnatal days 10-21. In previous work, only Pde6ß and vesicular-trafficking protein Prenylated Rab Acceptor 1 (PRA1) have been found to be consistently downregulated during the first ten days following birth. In a yeast-two-hybrid assay conducted by our lab, PRA1 was shown to interact with Charged Multivesicular Body Protein 2B (CHMP2B), an endosomal sorting protein that has been implicated in several neurodegenerative diseases, such as frontotemporal dementia and amyotrophic lateral sclerosis. We investigated whether CHMP2B is mislocalized in the rd1 mouse. Immunohistochemical labeling of CHMP2B was done in both postnatal wild type and rd1 mouse retinas. Prior to the onset of degeneration, CHMP2B immunolabeling was weaker in rd1 retinas, particularly in the developing photoreceptor synaptic layer, compared to wild type. Furthermore, staining of CHMP2B in wild type photoreceptors peaked at postnatal day 12, while CHMP2B staining in rd1 retinas was diffuse and disorganized. In conclusion, these findings show that proper localization of CHMP2B is disrupted in rd1 photoreceptors. Further studies are needed to investigate possible roles for CHMP2B in endocytic activity that is vital to photoreceptor maintenance, as well as differentiation, and development in mouse photoreceptors.

Hinge action versus grip in translocation by RNA polymerase.

Based on molecular dynamics simulations and functional studies, a conformational mechanism is posited for forward translocation by RNA polymerase (RNAP). In a simulation of a ternary elongation complex, the clamp and downstream cleft were observed to close. Hinges within the bridge helix and trigger loop supported generation of translocation force against the RNA-DNA hybrid resulting in opening of the furthest upstream i-8 RNA-DNA bp, establishing conditions for RNAP sliding. The ß flap tip helix and the most N-terminal ß' Zn finger engage the RNA, indicating a path of RNA threading out of the exit channel. Because the ß flap tip connects to the RNAP active site through the ß subunit double-Ψ-ß-barrel and the associated sandwich barrel hybrid motif (also called the flap domain), the RNAP active site is coupled to the RNA exit channel and to the translocation of RNA-DNA. Using an exonuclease III assay to monitor translocation of RNAP elongation complexes, we show that K+ and Mg2+ and also an RNA 3'-OH or a 3'-H2 affect RNAP sliding. Because RNAP grip to template suggests a sticky translocation mechanism, and because grip is enhanced by increasing K+ and Mg2+concentration, biochemical assays are consistent with a conformational change that drives forward translocation as observed in simulations. Mutational analysis of the bridge helix indicates that 778-GARKGL-783 (Escherichia coli numbering) is a homeostatic hinge that undergoes multiple bends to compensate for complex conformational dynamics during phosphodiester bond formation and translocation.

The antiepileptic and ictogenic effects of optogenetic neurostimulation of PV-expressing interneurons.

Parvalbumin (PV)-expressing interneurons exert powerful inhibitory effects on the normal cortical network; thus optogenetic activation of PV interneurons may also possess antiepileptic properties. To investigate this possibility we expressed channelrhodopsin 2 in PV interneurons by locally injecting the Cre-dependent viral vector AAV2/1-EF1a-DIO-ChETA-EYFP into the S1 barrel cortex of PV-Cre mice. Approximately 3-4 wk later recurrent electrographic seizures were evoked by local application of the chemoconvulsant 4-aminopyridine (4-AP); the ECoG and unit activity were monitored with extracellular silicone electrodes; and PV interneurons were activated optogenetically during the ictal and interictal phases. Five- to ten-second optogenetic activation of PV interneurons applied during electrographic seizures (ictal phase) terminated 33.7% of electrographic seizures compared with only 6% during sham stimulation, and the average electrographic seizure duration shortened by 38.7 ± 34.2% compared with sham stimulation. In contrast, interictal optogenetic activation of PV interneurons showed powerful and robust ictogenic effects. Approximately 60% of interictal optogenetic stimuli resulted in electrographic seizure initiation. Single-unit recordings revealed that presumptive PV-expressing interneurons markedly increased their firing during optogenetic stimulation, while many presumptive excitatory pyramidal neurons showed a biphasic response, with initial suppression of firing during the optogenetic pulse followed by a synchronized rebound increase in firing at the end of the laser pulse. Our findings indicated that ictal activation of PV-expressing interneurons possesses antiepileptic properties probably due to suppression of firing in pyramidal neurons during the laser pulse. However, in addition interictal activation of PV-expressing interneurons possesses powerful ictogenic properties, probably due to synchronized postinhibition rebound firing of pyramidal neurons.

Phosphodiesterase 6ß Expression In Developing Mouse Retina.

The rd1 mouse is a well-studied model of retinitis pigmentosa (RP), an inherited retinal degenerative disease affecting approximately 1 in 4000 people. It is characterized by a mutation in the Pde6b gene that codes for Phosphodiesterase 6ß (PDE6ß), a downstream effector of phototransduction. Pde6b gene expression occurs embryonically in mouse retina, whereas other proteins involved in phototransduction are expressed around postnatal day 5 (P5). The primary aim of this study is to investigate the temporal and spatial expression pattern of PDE6ß protein during photoreceptor development. Using Western blots with wild type and rd1 mouse retinas from P2 - P21 we demonstrated that PDE6ß protein is expressed in wild type retinas by P2 and is not detected in rd1 retinas. The earliest detection of PDE6ß in wild type retinas by immunohistochemistry was at P6, where it was confined to the apical region of the photoreceptor layer. The expression of PDE6ß protein prior to differentiation of photoreceptor cells and prior to expression of other phototransduction proteins is consistent with the hypothesis that PDE6ß may play a role during photoreceptor development distinct from its role in phototransduction. Our lab previously showed that Prenylated Rab Acceptor 1 (PRA1), a vesicular trafficking protein, is downregulated in the developing rd1 retina, although its function in the retina is unknown. The second aim of this study was to explore the relationship between PRA1 and PDE6ß. We used immunohistochemistry to determine whether the two proteins are co-localized during the postnatal differentiation period. However, no co-localization between PDE6ß and PRA1 was detected. The function of PRA1 in developing retina remains to be elucidated.

The RNA polymerase bridge helix YFI motif in catalysis, fidelity and translocation.

The bridge α-helix in the ß' subunit of RNA polymerase (RNAP) borders the active site and may have roles in catalysis and translocation. In Escherichia coli RNAP, a bulky hydrophobic segment near the N-terminal end of the bridge helix is identified (ß' 772-YFI-774; the YFI motif). YFI is located at a distance from the active center and adjacent to a glycine hinge (ß' 778-GARKG-782) involved in dynamic bending of the bridge helix. Remarkably, amino acid substitutions in YFI significantly alter intrinsic termination, pausing, fidelity and translocation of RNAP. F773V RNAP largely ignores the λ tR2 terminator at 200µM NTPs and is strongly reduced in λ tR2 recognition at 1µM NTPs. F773V alters RNAP pausing and backtracking and favors misincorporation. By contrast, the adjacent Y772A substitution increases fidelity and exhibits other transcriptional defects generally opposite to those of F773V. All atom molecular dynamics simulation revealed two separate functional connections emanating from YFI explaining the distinct effects of substitutions: Y772 communicates with the active site through the link domain in the ß subunit, whereas F773 communicates through the fork domain in the ß subunit. I774 interacts with the F-loop, which also contacts the glycine hinge of the bridge helix. These results identified negative and positive circuits coupled at YFI and employed for regulation of catalysis, elongation, termination and translocation.

Long-term behavioral and biochemical effects of an ultra-low dose of Δ9-tetrahydrocannabinol (THC): neuroprotection and ERK signaling.

We have previously reported that a single injection of an ultra-low dose of delta-9-tetrahydrocannabinol (THC; the psychoactive ingredient of marijuana) protected the brain from pentylenentetrazole (PTZ)-induced cognitive deficits when applied 1-7 days before or 1-3 days after the insult. In the present study we expanded the protective profile of THC by showing that it protected mice from cognitive deficits that were induced by a variety of other neuronal insults, including pentobarbital-induced deep anesthesia, repeated treatment with 3,4 methylenedioxymethamphetamine (MDMA; "ecstasy") and exposure to carbon monoxide. The protective effect of THC lasted for at least 7 weeks. The same ultra-low dose of THC (0.002 mg/kg, a dose that is 3-4 orders of magnitude lower than the doses that produce the known acute effects of the drug in mice) induced long-lasting (7 weeks) modifications of extracellular signal-regulated kinase (ERK) activity in the hippocampus, frontal cortex and cerebellum of the mice. The alterations in ERK activity paralleled changes in its activating enzyme MEK and its inactivating enzyme MKP-1. Furthermore, a single treatment with the low dose of THC elevated the level of pCREB (phosphorylated cAMP response element-binding protein) in the hippocampus and the level of BDNF (brain-derived neurotrophic factor) in the frontal cortex. These long-lasting effects indicate that a single treatment with an ultra-low dose of THC can modify brain plasticity and induce long-term behavioral and developmental effects in the brain.

Pre- and post-conditioning treatment with an ultra-low dose of Δ9-tetrahydrocannabinol (THC) protects against pentylenetetrazole (PTZ)-induced cognitive damage.

Preconditioning, a phenomenon where a minor noxious stimulus protects from a subsequent more severe insult, and post-conditioning, where the protective intervention is applied following the insult, offer new insight into the neuronal mechanism(s) of neuroprotection and may provide new strategies for the prevention and treatment of brain damage. We have previously reported that a single administration of an extremely low dose of Δ(9)-tetrahydrocannabinol (THC; the psychoactive ingredient of marijuana) to mice induced minor long-lasting cognitive deficits. In the present study we examined the possibility that such a low dose of THC will protect the mice from more severe cognitive deficits induced by the epileptogenic drug pentylenetetrazole (PTZ). THC (0.002 mg/kg, a dose that is 3-4 orders of magnitude lower than the doses that induce the conventional effects of THC) was administered 1-7 days before, or 1-3 days after the injection of PTZ (60 mg/kg). The consequences of this treatment were studied 3-7 weeks later by various behavioral tests that evaluated different aspects of memory and learning. We found that a single administration of THC either before or after PTZ abolished the PTZ-induced long-lasting cognitive deficits. Biochemical studies indicated a concomitant reduction in phosphorylated-ERK (extracellular signal-regulated kinase) in the cerebella of mice 7 weeks following the injection of THC. Our results suggest that a pre- or post-conditioning treatment with extremely low doses of THC, several days before or after brain injury, may provide safe and effective long-term neuroprotection.